Y.H. Ma

Adsorption, permeation, and diffusion of gases in microporous membranes. II. Permeation of gases in microporous glass membranes

The gas permeability properties of He, H2, CO2 O2, N2 and CH4 in microporous silica membranes were studied as a function of temperature and pressure. A mathetical model of compressible flow in a hollow fiber tube with permeable walls was developed and solved to describe gas transfer in the membranes. The permeation rate of He in the microporous membrane was comparable to that in industrially produced polymeric membranes. Selectivity factors in the membrane were found to be a function of differences in the gas kinetic diameters. The ideal selectivity factor for He/CH4 was more than 10,000 at 30°C. Selectivity factors decreased with increasing temperature.

Protein adsorption and fouling in ceramic ultrafiltration membranes

Abstract The adsorption of proteins to membrane surfaces can lead to the formation of a fouling layer, which drastically reduces permeate flux and represents a serious impediment to efficient ultrafiltration operations. In this work, the factors influencing permeate flux, adsorption and fouling during crossflow ultrafiltration of bovine serum albumin using microporous alumina membranes with mean pore diameters of 40, 350 and 1000 A have been examined. p]In general, the permeate flux was observed to be a function of concentration, transmembrane pressure and crossflow velocity as described by classical gel polarization theory. For protein concentrations above 1 g/l, solute rejection was nearly complete even for the 1000 A membranes. At low solute concentrations, rejection increased with decreasing pore size and increasing crossflow velocity. p]Studies of the flux and rejection dependence on pH, solute concentration, ionic strength, membrane pore size and cleaning procedure, coupled with adsorption studies, indicated that adsorption-related pore plugging plays a significant role in the two larger pore size membranes.

Oxidative coupling of methane in porous Vycor membrane reactors

Abstract Porous Vycor membrane tubes were used in shell-and-tube type membrane reactors to study the effect on the oxidative coupling of methane of metering the oxygen into the catalyst bed. Experimental studies showed that under conditions of complete oxygen conversion, Vycor membrane reactors packed with Sm 2 O 3 catalyst exhibited enhanced hydrocarbon (C 2 ) selectivity. C 2 yields were comparable to those of the conventional co-feed packed bed reactors operated under the same conditions. The higher C 2 selectivity in the membrane reactors indicated that, for methane coupling, regulating the supply of oxygen along the length of the packed bed may be beneficial to C 2 formation.

Adsorption, diffusion and permeation of gases in microporous membranes. III. Application of percolation theory to interpretation of porosity, tortuosity, and surface area in microporous glass membranes

The dependencies of porosity, surface area, and a tortuosity factor in microporous membranes on the porous membrane structure were considered. it was shown that the porosity and tortuosity in silica glasses could be described within the framework of the percolation theory. Tortuosity factors were influenced not only by the elongation of the diffusion path but also by the amount of throughout porosity. Mathematical medoling of gas diffusion processes in microporous glasses was performed by the MonteCarlo method. The simulation results were in good agreement with experimental observations for Vycor glass membranes. Dependence of the surface area per unit volume, SV, on pore size was represented by a simple power law of the type SV∼f (θ)d−1P with O < f(θ) < 1.23, where dP is the pore diameter. Experimental data from literature on surface area and porosity in porous carbons, alumina, silica, glasses, silver, nickel, and polymeric membranes were used to verify the relationship. As a first approximation, the surface area per unit volume in porous materials with porosity 0.4 < θ < 0.6 can be estimated as SV ≈ 1.23/dP.

Protein adsorption and fouling of ceramic membranes as measured by scanning electron microscopy with digital X-ray mapping

A technique for studying fouling in ceramic membranes using the energy dispersive x-ray spectroscopy capability of an electron microscope is described. The location and amount of foulant within the membrane are presented on a digital x-ray map showing elements constituent to or stained on the foulant. Fouling of alumina membranes during filtration of the protein hemoglobin has been studied as a function of filtration time, pH, and membrane pore size. After each filtration run, the protein within a piece of the membrane was stained with phosphotungstic acid and located on a digital map of either phosphorus or tungsten. For a 0.2 μm pore size membrane, time dependent fouling was observed consistent with an observed flux decline within the first few minutes of filtration. A pH dependence was also observed indicating much greater fouling at pH 6.9 near the protein isoelectric point than at pH 8.5. This observation is consistent with pH dependent adsorption, flux, and rejection studies. No internal fouling was...

A Comparative Study of Adsorption and Diffusion of Vapor Alcohols and Alcohols From Aqueous Solutions in Silicalite

The adsorption isotherms and intracrystalline diffusivities of vapor alcohols and alcohols from aqueous solutions in silicalite were experimentally determined. The adsorption isotherms for the alcohols in liquid phase are well predicted from the vapor phase isotherm data using the analogy theory. The intracrystalline diffusivities in liquid phase exhibit the same trend as those in the vapor phase at near saturation loading. The estimated difference of heats of immersion between alcohols and water in silicalite varies from 6.3 to 7.3 KJ/mol. The activation energy for liquid intracrystalline diffusion in silicalite ranges from 5.7 to 21 KJ/mol and increases with decreasing intracrystalline diffusivity.

Adsorption of Hydrocarbons in (Na, K)-ZSM5, -ZSM11 and “Al-Free” NaZSM5 and NaZSM11

The equilibrium adsorption and diffusion of methanol, n-hexane, 1,2,4-trimethylbenzene, and xylenes on different ZSM samples were studied at 303K and in the pressure range of P/P ° =0.0001 to 0.8. The effects of the presence of a small amount of Al in the ZSM samples were investigated by comparing the sorption data in “Al-free”-NaZSM5 and -NaZSM11 with those for NaZSM5 and NaZSM11. The effects of cations on adsorption and diffusion were also investigated. Furthermore, the adsorption data obtained for directly synthesized KZSM5 and KZSM11 were compared with those for KZSM5(ex) and KZSM11(ex), which were prepared through ion exchange with their respective Na-forms, to study the effects of methods of introducing exchangeable cations on adsorption and diffusion.

Adsorption of Proteins and Antibiotics on Porous Alumina Membranes

Abstract Adsorption of proteins and antibiotics within porous membranes can adversely affect membrane performance during recovery of these products using filtration. The adsorption of two proteins, bovine serum albumin and hemoglobin, and an antibiotic, tetracycline, on alumina membranes has been investigated. Protein adsorption and flux during filtration were observed to be pH dependent with maximum adsorption and minimum flux near the protein isoelectric points. Energy dispersive spectroscopy was used to locate and quantify adsorbed proteins within membrane cross sections after filtration. The pH dependence of adsorption was modeled by including the effects of protein-protein and protein-membrane charge interactions in the random sequential adsorption model.

Adsorption Equilibrium of Ethylene-Carbon Dioxide Mixture on Zeolite ZSM5

Binary gas mixture data for the ethylene-carbon dioxide system were obtained for cation exchanged forms of ZSM5 (Li + , Na + , K + , Rb + , Mg +2 , Ca +2 , Sr +2 and Ba +2 )for the gas phase CO 2 mole fraction of 0.766 at 308K and 101.3KPa. The experimental adsorption phase diagrams were obtained for CO 2 -C 2 H 4 on NaZSM5 and MgZSM5. Single component adsorption isotherms for CO 2 and C 2 H 4 were also obtained for these two zeolites. The single component data were used to obtain parameters derived in the vacancy solution model and the statistical thermodynamic model. These parameters were, in turn, used to predict binary mixture isotherms for these two zeolites. The agreement between experimental data and predicted values is generally good.